// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// WARNING: You should *NOT* be using this class directly.  PlatformThread is
// the low-level platform-specific abstraction to the OS's threading interface.
// You should instead be using a message-loop driven Thread, see thread.h.

#ifndef BASE_THREADING_PLATFORM_THREAD_H_
#define BASE_THREADING_PLATFORM_THREAD_H_

#include <stddef.h>

#include "base/base_export.h"
#include "base/macros.h"
#include "base/time/time.h"
#include "build/build_config.h"

#if defined(OS_WIN)
#include <windows.h>
#elif defined(OS_POSIX)
#include <pthread.h>
#include <unistd.h>
#endif

namespace base {

// Used for logging. Always an integer value.
#if defined(OS_WIN)
typedef DWORD PlatformThreadId;
#elif defined(OS_POSIX)
typedef pid_t PlatformThreadId;
#endif

// Used for thread checking and debugging.
// Meant to be as fast as possible.
// These are produced by PlatformThread::CurrentRef(), and used to later
// check if we are on the same thread or not by using ==. These are safe
// to copy between threads, but can't be copied to another process as they
// have no meaning there. Also, the internal identifier can be re-used
// after a thread dies, so a PlatformThreadRef cannot be reliably used
// to distinguish a new thread from an old, dead thread.
class PlatformThreadRef {
public:
#if defined(OS_WIN)
    typedef DWORD RefType;
#elif defined(OS_POSIX)
    typedef pthread_t RefType;
#endif
    PlatformThreadRef()
        : id_(0)
    {
    }

    explicit PlatformThreadRef(RefType id)
        : id_(id)
    {
    }

    bool operator==(PlatformThreadRef other) const
    {
        return id_ == other.id_;
    }

    bool is_null() const
    {
        return id_ == 0;
    }

private:
    RefType id_;
};

// Used to operate on threads.
class PlatformThreadHandle {
public:
#if defined(OS_WIN)
    typedef void* Handle;
#elif defined(OS_POSIX)
    typedef pthread_t Handle;
#endif

    PlatformThreadHandle()
        : handle_(0)
    {
    }

    explicit PlatformThreadHandle(Handle handle)
        : handle_(handle)
    {
    }

    bool is_equal(const PlatformThreadHandle& other) const
    {
        return handle_ == other.handle_;
    }

    bool is_null() const
    {
        return !handle_;
    }

    Handle platform_handle() const
    {
        return handle_;
    }

private:
    Handle handle_;
};

const PlatformThreadId kInvalidThreadId(0);

// Valid values for priority of Thread::Options and SimpleThread::Options, and
// SetCurrentThreadPriority(), listed in increasing order of importance.
enum class ThreadPriority : int {
    // Suitable for threads that shouldn't disrupt high priority work.
    BACKGROUND,
    // Default priority level.
    NORMAL,
    // Suitable for threads which generate data for the display (at ~60Hz).
    DISPLAY,
    // Suitable for low-latency, glitch-resistant audio.
    REALTIME_AUDIO,
};

// A namespace for low-level thread functions.
class BASE_EXPORT PlatformThread {
public:
    // Implement this interface to run code on a background thread.  Your
    // ThreadMain method will be called on the newly created thread.
    class BASE_EXPORT Delegate {
    public:
        virtual void ThreadMain() = 0;

    protected:
        virtual ~Delegate() { }
    };

    // Gets the current thread id, which may be useful for logging purposes.
    static PlatformThreadId CurrentId();

    // Gets the current thread reference, which can be used to check if
    // we're on the right thread quickly.
    static PlatformThreadRef CurrentRef();

    // Get the handle representing the current thread. On Windows, this is a
    // pseudo handle constant which will always represent the thread using it and
    // hence should not be shared with other threads nor be used to differentiate
    // the current thread from another.
    static PlatformThreadHandle CurrentHandle();

    // Yield the current thread so another thread can be scheduled.
    static void YieldCurrentThread();

    // Sleeps for the specified duration.
    static void Sleep(base::TimeDelta duration);

    // Sets the thread name visible to debuggers/tools. This will try to
    // initialize the context for current thread unless it's a WorkerThread.
    static void SetName(const std::string& name);

    // Gets the thread name, if previously set by SetName.
    static const char* GetName();

    // Creates a new thread.  The |stack_size| parameter can be 0 to indicate
    // that the default stack size should be used.  Upon success,
    // |*thread_handle| will be assigned a handle to the newly created thread,
    // and |delegate|'s ThreadMain method will be executed on the newly created
    // thread.
    // NOTE: When you are done with the thread handle, you must call Join to
    // release system resources associated with the thread.  You must ensure that
    // the Delegate object outlives the thread.
    static bool Create(size_t stack_size,
        Delegate* delegate,
        PlatformThreadHandle* thread_handle)
    {
        return CreateWithPriority(stack_size, delegate, thread_handle,
            ThreadPriority::NORMAL);
    }

    // CreateWithPriority() does the same thing as Create() except the priority of
    // the thread is set based on |priority|.
    static bool CreateWithPriority(size_t stack_size, Delegate* delegate,
        PlatformThreadHandle* thread_handle,
        ThreadPriority priority);

    // CreateNonJoinable() does the same thing as Create() except the thread
    // cannot be Join()'d.  Therefore, it also does not output a
    // PlatformThreadHandle.
    static bool CreateNonJoinable(size_t stack_size, Delegate* delegate);

    // Joins with a thread created via the Create function.  This function blocks
    // the caller until the designated thread exits.  This will invalidate
    // |thread_handle|.
    static void Join(PlatformThreadHandle thread_handle);

    // Detaches and releases the thread handle. The thread is no longer joinable
    // and |thread_handle| is invalidated after this call.
    static void Detach(PlatformThreadHandle thread_handle);

    // Toggles the current thread's priority at runtime. A thread may not be able
    // to raise its priority back up after lowering it if the process does not
    // have a proper permission, e.g. CAP_SYS_NICE on Linux. A thread may not be
    // able to lower its priority back down after raising it to REALTIME_AUDIO.
    // Since changing other threads' priority is not permitted in favor of
    // security, this interface is restricted to change only the current thread
    // priority (https://crbug.com/399473).
    static void SetCurrentThreadPriority(ThreadPriority priority);

    static ThreadPriority GetCurrentThreadPriority();

private:
    DISALLOW_IMPLICIT_CONSTRUCTORS(PlatformThread);
};

} // namespace base

#endif // BASE_THREADING_PLATFORM_THREAD_H_
